Polyamide fiber with enhanced dyeing properties, process for obtaining such fiber and polyamide article made therefrom

ABSTRACT

The present invention relates to a polyamide fiber with enhanced dyeing properties. The polyamide fiber is suitable for low-temperature dyeing and shorter dyeing cycle. The present invention also discloses a method for obtaining such a fiber. The polyamide fiber is obtained by blending at least a polyamide 5.X, X being an integer from 4 to 16 with an aliphatic polyamide during the melt-spinning extrusion of the polyamide fiber. The blended polyamide fiber and articles made therefrom can be dyed at a lower temperature than the usual boiling temperature, and the dyeing time is half of the time of a normal dyeing cycle. The dyed polyamide fiber and article also show enhanced fastness to washing and perspiration.

PREVIOUS ART

The commercial interest in polyamides, particularly based on fibers and yarns used in textile goods such as underwear, sportswear, leisurewear and nightwear, has been extensively increased because of theirs advantages in this field, like easy-care, fast-drying properties, high durability, excellent physical properties, abrasion resistance, balanced moisture absorption, good elasticity, lightness, comfort and softness.

Polyamide, also known as nylon, is a linear condensation polymer composed of repeated primary bonds of amide group. A polyamide fiber is generally produced by melt-spinning extrusion and is available in staple fiber, tow, monofilament, multi-filament, flat or texturized form. Polyamides are semi-crystalline polymers. The amide group —(—CO—NH—)— provides hydrogen bonding between polyamide intermolecular chains, providing high strength at elevated temperatures, toughness at low temperatures, wear and abrasion resistance, low friction coefficient and good chemical resistance. These properties have made polyamides among the strongest of all available man-made fibers.

The dyeing efficiency of polyamide fibers is related to the carboxyl end groups —COON and especially amine end groups —NH2, which exhibit polar and hydrophilic characteristics. The dye diffusion into fibers is related to the amorphous and crystalline balance, molecular orientation, molecular weight, intra-molecular and inter-molecular bonds and available hydroxyls or polar groups.

The dye color uptake, rate of dyeing, homogeneity and fastness depend on the dyeing process conditions such as temperature, time and pH, and also on the dyeing equipment like exhaust or padding equipment. The chemical auxiliaries, for instance, leveling agent, surfactant, retarders, fixing and so forth, are also important for an effective dyeing.

The dye is classified according to its chemical composition, mechanism of reaction, size of molecules and so on. The most common types of dyes are reactive dyes, direct dyes, basic dyes, acid dyes, metallic dyes, azo dyes, dispersed dyes and vat dyes. Polyamides contain primary amino end-groups that are more suitable for acid dyes, for which the best dye uptake and fastness is obtained. The acid dye contains hydrophilic groups of sodium sulfonate radicals (—SO₃Na) that can be combined with the amino groups (—NH+) of the polyamide fiber by the ionic bonds or electrostatic forces to provide better dyeability and brighter color. The rest of the aforementioned dyes are combined with polyamide fiber by hydrogen bonds or Van der Waals forces to provide a lighter color. For instance, when polyamide is dyed with dispersed dyes, the color build-up is unaffected by chemical variations of the fiber, hence yielding more uniform color. However, the use of dispersed dyes on polyamide is restricted to pale shades because of poor color build-up and fastness properties as the dispersed dye is an insoluble dye that diffuses into the fiber interior rather than combining by chemical interactions.

The common temperature and process time for dyeing polyamide is boiling temperature (˜100° C.) and 60 minutes of processing time. This temperature is known as necessary to generate a swollen morphological structure of the fiber, by spacing the molecules and breaking the intermolecular bonds so that the dye can diffuse into the interior of the fiber and form permanent chemical bonds. The time of 60 minutes is known to be required for achieving a deep, regular and homogenous color. However, those temperatures and time are energy consuming and not environment friendly.

Several attempts have been made to optimize the dyeing process so as to reduce time, temperature, energy, chemical auxiliaries and water in order to improve efficiency, productivity and reduce carbon footprint. In addition, there have been initiatives to modify the chemical composition of the dyes, making them more sustainable and efficient for optimized dyeing conditions. Experiments have also been carried out to increase the affinity of the aliphatic polyamide for anionic dyes by increasing the amino end group content. These approaches lead to a deeper dark color but don't aim at reducing the dyeing temperature and time.

In view of the above, up to now there is no solution for improving dyeing properties of a polyamide, such as intrinsic low-temperature and faster dyeing properties.

BRIEF DESCRIPTION OF THE INVENTION

Therefore, the present invention aims to find a solution for obtaining a polyamide article that is dyed with significantly lower temperature and time and that yields a dark, homogenous and durable color; and surprisingly, the inventors have found that a specific polyamide fiber blend has enhanced dyeing capabilities such as low-temperature dyeing of dark and light colors and reduced dyeing time.

The present invention thus provides a polyamide fiber with enhanced dyeing properties, wherein the polyamide fiber is a blend of at least two different polyamides: a first polyamide and second polyamide,

-   -   the first polyamide being an aliphatic polyamide selected from         the group consisting of polyamide 6, polyamide 6.6, polyamide         6.9, polyamide 6.12, polyamide 6.10, polyamide 11, polyamide 12,         polyamide 10.10, polyamide 4.6, polyamide 4.10, polyamide 12.12,         polyamide 10.12 and mixtures thereof, and     -   the second polyamide being selected between polyamide 5.X, X         being an integer from 4 to 16 and mixtures thereof.

Surprisingly, the intrinsic morphological properties of the polyamide are changed, mainly the intermolecular amide bonds, making the polyamide fiber susceptible to swelling and chemical interactions at lower temperatures. Therefore, uniform, dark and durable colors are possible to be achieved at a more efficient and environmentally friendly process.

The present invention also aims at a method for obtaining said polyamide fiber with enhanced dyeing properties, wherein the polyamide fiber is obtained by melt-spinning extrusion of at least the first and the second polyamide as defined above and below in the specification.

Also, the present invention proposes a polyamide article comprising the polyamide fiber with enhanced dyeing properties as defined above and below in the following paragraphs; and a method for obtaining such a polyamide article, wherein the polyamide fiber of the invention is transformed by texturizing, drawing, warping, knitting, weaving, nonwoven processing, garment manufacturing or a combination thereof.

Then, another object of the present invention is the use of a second polyamide being a polyamide 5.X, X being an integer from 4 to 16 or mixtures thereof in combination with at least a first polyamide being an aliphatic polyamide selected from the group consisting of polyamide 6, polyamide 6.6, polyamide 6.9, polyamide 6.12, polyamide 6.10, polyamide 11, polyamide 12, polyamide 10.10, polyamide 4.6 polyamide 4.10, polyamide 12.12, polyamide 10.12 and mixtures thereof in order to enhance the dyeing properties of a polyamide fiber made therefrom.

DETAILED DESCRIPTION OF THE INVENTION Definitions

The expression “polyamide fiber” in the sense of the present invention is the generic term including the following spun articles: a fiber, a monofilament, a multifilament and a yarn. A “polyamide article” according to the invention is a transformed or treated polyamide fiber and includes staple fibers, any flock or any textile composition made of polyamide fiber, especially fabrics and/or garments. In the below description, the terms “fiber”, “yarn” and “filament” can be used indifferently without changing the meaning of the invention.

Polyamide Fiber with Enhanced Dyeing Properties

The present invention provides a polyamide fiber blend with enhanced dyeing capabilities, such as faster and low-temperature dyeing of dark and light colors. The polyamide fiber with enhanced dyeing properties according to the invention is a blend of at least two different polyamides: a first polyamide and second polyamide.

First Polyamide

The first polyamide is an aliphatic polyamide composed of AB and/or AABB type, selected from the group consisting of polyamide 6, polyamide 6.6, polyamide 6.9, polyamide 6.12, polyamide 6.10, polyamide 11, polyamide 12, polyamide 10.10, polyamide 4.6, polyamide 4.10, polyamide 12.12, polyamide 10.12 and mixtures thereof.

It is preferably selected from the group consisting of polyamide 6 or polyamide 6.6 and mixtures thereof; and even more preferably poly(hexamethylene adipamide) (polyamide 6.6 or Nylon 6.6).

The above polyamides are well known in the art and can be obtained by polycondensation of a mixture of diacids and diamines monomers or a salt thereof, which are commercially available. The diamines and diacids of polyamide AABB type belong to the group of tetramethylenediamine (1,4-diaminobutane or putrescine), hexamethylenediamine (1,6-hexanediamine), dodecamethylenediamine (1,12- diaminododecane), hexanedioic acid (adipic acid), nonanedioic acid (azelaic acid), decanedioic acid (sebacic acid), undecanedioic acid, dodecanedioic acid. The monomers of the polyamide AB type belong to the group of caprolactam, 11-aminoundecanoamide, dodecanolactam or laurolactam.

In the case of poly(hexamethylene adipamide) (polyamide 6.6), the main monomers are hexamethylenediamine and adipic acid. However, these monomers can comprise up to 25 mol % of other diamine or diacid monomers or even amino acid or lactam monomers.

In particular, the amino acid is aminocaproic acid and the lactam is caprolactam.

The preferred first polyamides may have a viscosity index (IVN) in the range of 100 to 200 ml/g, preferably between about 120 and 170. This IVN is measured according to the standard ISO 307, which is explained hereinafter in the experimental part.

The amino terminal groups (ATG) content of those polyamides is advantageously from 25 to 60 equivalent/ton, and the carboxyl terminal groups (CTG) is advantageously from 45 to 90 equivalent/ton. Those amino/carboxyl end groups contents are measured according to the methodology explained hereinafter in the experimental part.

The opacity of this first polyamide can be brilliant, semi-dull, full-dull and mixtures thereof. The opacity is related to the amount of titanium dioxide present in the polymer, which is relevant for dyeability, lustre and processability issues. For instance, brilliant has lower amount of titanium dioxide, whereas full-dull has higher amount of titanium dioxide.

A particularly preferred first polyamide according to the present invention is a polyamide 6.6 containing from 1 to 5% of caprolactam. This polyamide has advantageously a IVN (viscosity index) from 128 to 132, and ATG (amine terminal groups) from 40 to 45 and is a full-dull polymer.

Second Polyamide

The second polyamide is a polyamide 5.X, X being an integer from 4 to 16 and mixtures thereof. More preferably, the second polyamide is an odd/even polyamide such as polyamide 5.4, 5.6, 5.8, 5.10, 5.12, 5.14. In a preferred embodiment, the second polyamide of the polyamide fiber according to the invention is polyarnide 5.6 or polyamide 5.10. The best results in terms of dyeing properties are obtained when the second polyamide is polyamide 5.6.

Polyamide 5.X is made of pentamethylenediamine and an aliphatic dicarboxylic acid(s) as raw materials.

The list of potential dicarboxylic acids is the following: butanedioic acid (succinic acid), pentanedioic acid (glutaric acid), hexanedioic acid (adipic acid), heptanedioic acid (pimelic acid), octanedioic acid (suberic acid), nonanedioic acid (azelaic acid), decanedioic acid (sebacic acid), undecanedioic acid, dodecanedioic acid, brassylic acid, tetradecanedioic acid, pentadecanedioic acid, hexadecanedioic acid.

All those diacids are commercially available.

Polyamides 5.6 and 5.10 have the, advantage of being able to be manufactured from biomass according to ASTM6866. As pentamethylenediamine can also be prepared from bio-resources according to ASTM6866, the resulting polyamide can be at least 45% bio-sourced and up to 100% from bio-resources.

Polyamide 5.6 is also known as poly(pentamethylene adipamide), which consists of pentamethylenediamine and adipic acid as raw materials.

The preferred polyamide 5.6 may have a viscosity index (IVN) in the range of 100 to 200 ml/g, preferably between about 120 and 170. This IVN is measured according to the standard ISO 307, which is explained hereinafter in the experimental part.

The amino terminal groups (ATG) content is advantageously from 25 to 60 equivalent/ton, and the carboxylic terminal groups (CTG) content is preferably from 45 to 90 equivalent/ton.

Those amino/carboxyl end groups contents are measured according to the methodology explained hereinafter in the experimental part.

The opacity of this second polyamide can be brilliant, semi-dull, full-dull and mixtures thereof, as explained above for the first polyamide.

A particularly preferred polyamide 5.6 according to the present invention has a IVN (viscosity index) of from 138 to 142, and ATG (amine terminal groups) from 38 to 42 and is a brilliant polymer, that is, the polyamide contains no titanium dioxide.

A polyamide fiber according to the invention is particularly advantageous when the second polyamide is present in an amount of about 1.0% to 40.0%, preferably about 5.0 to 20.0% by weight of the total weight of the polyamide fiber. The best mode is when the second polyamide, in particular polyamide 5.6, is present in an amount of 5% to 10% by weight of the total weight of the polyamide fiber.

The polyamide fiber according to the invention has advantageously an overall dtex of about 40 to 300, and a dpf (dtex per filament) of about 1 to 5. The tenacity (elongation at break) is from 30 to 80 cN/dtex. The elongation at break is from 20% to 90%.

Indeed, the combination of the above preferred technical features of the first and second polyamide allow obtaining an even better dyeing behavior in combination with sufficient and satisfactory mechanical properties of the fiber for a textile application.

Process for Obtaining a Polyamide Fiber with Enhanced Dyeing Properties

The invention also provides a method for obtaining the polyamide fiber as described above. The method involves forming the polyamide fiber blend by melt-spinning extrusion, with at least the first and second polyamides described above.

According to the invention the expression “melt-spinning” is understood to mean the extrusion process of converting the polyamide in a melt form into polyamide fibers. The polyamide(s) may be fed to the melt-spinning device in pellet, powder or melt form. The method includes any conventional extrusion spinning means suitable for melt-spinning extrusion of polyamide, these means being well known by a person skilled in the art, such as single-screw extruder, double-screw extruder, bi-component extruder and grid spinning head. The melt-spinning extrusion is further defined as being LOY (low-oriented yarn), POY (partially oriented yarn), FDY (fully drawn yarn), FOY (fully oriented yarn), LDI (Low denier Industrial) or HDI (High denier Industrial).

First Embodiment

According to a first embodiment, the melt spinning extrusion comprises the following steps:

-   -   a1. Feeding the first polyamide as a melt, pellet or powder into         the inlet of a screw extruder or grid spinning head,     -   a2. Melting, homogenizing and pressurizing the polyamide,     -   a3. Spinning the molten polyamide into a fiber,     -   a4. Cooling down the fiber and winding.         wherein the second polyamide is continuously introduced during         step al as a pellet or powder, preferably with the use of a         dosing apparatus.

As mentioned above, the second polyamide is preferably continuously introduced during step al of the single-screw extruder. It can be added as a polyamide pellet or powder, by means of a dosing apparatus like a dosing pump or a gravimetric feeding apparatus, preferably a gravimetric feeding apparatus. According to this embodiment, the second polyamide is melt-mixed with the first polyamide, before the formation of the fiber. The second polyamide can be optionally dried before being introduced in step a1.

In a particularly embodiment of the present invention, the second polyamide is continuously introduced as a pellet by means of a gravimetric feeding apparatus and the quantity added is 5% by weight of the total weight of the polyamide fiber.

The best results are obtained in the preferred embodiment wherein the second polyamide is continuously introduced as a pellet by means of a gravimetric feeding apparatus and the quantity added is 10% by weight of the total weight of the polyamide fiber.

Second Embodiment

According to a second embodiment, the melt-spinning extrusion comprises the following steps:

-   -   a′1. Feeding a blend of at least the first and the second         polyamides as a melt, pellet or powder into the inlet of a screw         extruder or grid spinning head,     -   a2. Melting, homogenizing and pressurizing the polyamide,     -   a3. Spinning the molten polyamide into a fiber,     -   a4. Cooling down the fiber and winding.         wherein the blend of at least the first and the second         polyamides is obtained by a step a0 previous to step a′1, and         comprising a polymerization of diacids and diamines monomers         corresponding to at least the first and the second polyamides or         salts thereof.

The polymerization at step a0 generally comprises the following steps: 1—concentration of the nylon salt by evaporation of water, in which the nylon salt is a combination of diacids and diamines monomers corresponding to at least the first and the second polyamides or salts thereof; 2—polymerization, under pressure, of the concentrated nylon salt; 3—Reduction in pressure of the polymerization medium in order to remove the residual water by evaporation; 4—Optional maintenance of the polymer temperature, at atmospheric pressure or under reduced pressure, in order to obtain the desired degree of polymerization; 5—Recovery of the polyamide as a melt or transformation of the molten polyamide into pellets.

Third Embodiment

According to a third embodiment, the melt-spinning extrusion comprises the following steps:

-   -   a1. Feeding the first polyamide as a melt, pellet or powder into         the inlet of a screw extruder or grid spinning head,     -   a2. Melting, homogenizing and pressurizing the polyamide,     -   a3. Spinning the molten polyamide into a fiber,     -   a4. Cooling down the fiber and winding.

Wherein the second polyamide is preferably continuously introduced as a polyamide melt during step a3 of the screw extruder, preferably a single-screw extruder. It is added, by means of an additional screw extruder, preferably a single-screw extruder. According to this embodiment, the second polyamide is blended with the first polyamide upon leaving the spinning pack spinneret, at the formation of the fiber, thereby forming a bi-component fiber.

All Embodiments

In the method according to the invention, according to any of the first or second or third embodiment described above, the second polyamide is advantageously introduced in an amount of 1.0% to 40.0%, preferably 5.0 to 20.0% by weight of the total weight of the polyamide fiber.

In steps a2 and a3, the term “polyamide” also means “polyamide blend”, as at least both the first and second polyamide are present.

In step a2, the polyamide (or polyamide blend) is melted, homogenized and pressurized inside the screw extruder, preferably at a temperature from 280 to 310° C., which is above the melting temperature of the first and second polyamides, and at a extrusion pressure from 30 to 70 bar.

Then, according to step a3, the molten polyamide (or polyamide blend) is spun into fibers (or yarns or filaments) preferably at a temperature from 260 to 310° C., spinning pack pressure from 150 to 250 and a spinning pack flow rate from 3 to 8 kg/h, with the use of a spinning screen-pack containing filtering elements and a spinneret.

Step a4 is the step of cooling down the fibers (or yarns or filaments) until the solidified form and winding the polyamide fibers into bobbins. A spinning oil can also be added onto the fiber at this step.

In the present invention, the extruder can be equipped with a metering system and/or additional single-screw extruder for introducing polymers and optionally additives such as masterbatches into the main polymer, at step a1 and/or a3 and/or a4.

Additives can be introduced during the method of the invention or may be present in the first and second polyamide pellet. The additives are selected from: antioxidants, stabilizers such as heat or light stabilizers, colorants, pigments, nucleating agents such as talc, matifying agents such as titanium dioxide or zinc sulphide, processing aids, biocides, viscosity modifiers, catalysts, Far Infrared Rays emitting minerals, biodegradable “converting” additives, anti-static additives, functional additives, optical brightening agents, nanocapsules, anti-bacterial, anti-mite, anti-fungi or other conventional additives. These additives are generally added in the polymer or at step al and/or a4 of the melt-spinning extrusion, in an amount of 0.001% to 10% by weight of the polyamide article.

The resulting polyamide fiber obtained according to the first, second and third embodiment described above can be dyed.

The enhanced dyeing properties are generally obtained with dyes consisting of reactive dyes, direct dyes, acid dyes and metallic dyes, preferably with reactive dyes or acid dyes.

These dyes combine with polyamide fiber by chemical reactions and will therefore benefit from a faster and lower temperature of dyeing, where the molecular structure is capable of forming chemical bonds. In a preferred embodiment of the present invention, acid dyes are advantageously used due to their high compatibility with polyamide amine end-groups.

In case the polyamide fiber obtained according to the first, second or third embodiment described above is dyed, the dyeing is performed at a temperature from 40° C. to 80° C., preferably at 60° C.±5° C.

In case the polyamide fiber obtained according to the first, second or third embodiment described above is dyed; the dyeing is preferably performed with a dyeing cycle from 20 to 40 minutes, preferably from 30 minutes ±5 minutes.

Polyamide Article

The polyamide fiber according to the invention can then be transformed into a polyamide article, notably a textile fabric and/or garment.

A polyamide article according to the invention is preferably a fiber, a staple fiber, a flock, a woven, a knitted or non-woven fabric or a textile article made from the polyamide fiber of the invention (defined above) or obtained from the process according to the invention.

The textile article may be any textile article known in the art including, but not limited to woven fabric, knitted fabric, nonwoven fabric, ropes, cords, sewing thread, and so forth.

The polyamide article is preferably dyed, notably with acid dyes.

The enhanced dyeing properties are generally obtained with dyes consisting of reactive dyes, direct dyes, acid dyes and metallic dyes. These dyes combine with polyamide fiber by chemical reactions and will therefore benefit from a faster and lower temperature of dying, where the molecular structure is capable of forming chemical bonds. Most preferably, reactive dyes and acid dyes. In a preferred embodiment of the present invention, acid dyes are advantageously used due to their high compatibility with polyamide amine end-groups.

Method for Obtaining a Polyamide Article

The methods for transforming the polyamide fiber into a polyamide article like a textile fabric or garment are well known by the skilled person in the art. Indeed, the polyamide fiber can be transformed into a polyamide article by texturizing, drawing, warping, knitting, weaving, nonwoven processing, garment manufacturing or a combination thereof.

The method for obtaining a polyamide article can further comprises a dyeing step. The enhanced dyeing properties are generally obtained with dyes consisting of reactive dyes, direct dyes, acid dyes and metallic dyes. These dyes combine with polyamide fiber by chemical reactions and will therefore benefit from a faster and lower temperature of dying, where the molecular structure is capable of forming chemical bonds. Most preferably, reactive dyes and acid dyes are chosen for the dyeing step. In a preferred embodiment of the present invention, acid dyes are advantageously used due to their high compatibility with polyamide amine end-groups.

In case the polyamide article obtained according to the invention is dyed, the dyeing is performed at a temperature from 40° C. to 80° C., preferably at 60° C. ±5° C.

In case the polyamide article obtained according to the invention is dyed, the dyeing is performed with a dyeing cycle from 20 to 40 minutes, preferably from 30 minutes±5 minutes.

These articles are subsequently used in a large number of applications, in particular in carpets, rugs, upholstery, parachutes, tents, bags, hosiery, underwear, sportswear, outerwear and so on.

The advantages of the polyamide fibers and articles made therefrom according to the invention are that they have enhanced dyeing capabilities such as low-temperature dyeing of dark and light colors and reduced dyeing time. The dyeing is therefore, uniform, dark and durable colors are possible to be achieved at a more efficient and environmentally friendly process.

Other details or advantages of the invention will become more clearly apparent in the light of the examples given below.

Examples

A series of polyamide articles (Examples 1 to 12), including comparative polyamide articles (Example 1 to 9 and 12) are formed and evaluated for washing fastness, alkaline and acid perspiration fastness, CIE Lab color intensity “L”, IVN (viscosity index) and ATG (terminal amino groups).

Amino Terminal Group Content (ATG)

The amino end group (ATG) content was determined by a potentiometric titration method. The quantity of 2 grams of polyamide is added to about 70 ml of phenol 90% wt. The mixture is kept under agitation and temperature of 40° C. until complete dissolution of the polyamide. The solution is then titrated by 0.1N HCl at about 25° C. The result is reported as equivalent/ton (eq/ton). In the case of analyzing fibers and articles, any residue or spin-finish must be previously removed.

Solution Viscosity (IVN)

The determination of the solution viscosity (IVN) is performed according to ISO 307. The polyamide is dissolved in formic acid 90% wt at 25° C. at a concentration of 0.005g/ml, and its flow time is measured. The result is reported as ml/g.

Washing Fastness ISO 105-C06

The sample is washed at 40° C. for 30 minutes, using conventional detergent (4 g/l). It is then rinsed 3 times in separate portions of 100 ml of water. The sample is assessed according to a grey scale in relation to change of color (ISO 105-A02) and staining of the adjacent fabrics (ISO 105-A03). The grade varies from 0 to 5, being 0 “low” and 5 “high”.

Perspiration Fastness ISO 105-E04

Acid and alkaline perspirations were assessed. The samples were placed in contact with the standard adjacent fabrics (for color transfer) and immersed in simulated alkaline and acid solution (pH 8.0 and 5.5 respectively), drained and placed between two plates under a specific pressure, temperature and time (37±2² C, 4 hours, pressure of 5 kg) in a testing device (perspirometer). The change in color of the samples and staining of the adjacent fabric is assessed with the Grey scales for color change (ISO 105-A02) and staining (ISO 105-A03). The grade varies from 0 to 5, being 0 “low” and 5 “high”.

Color Intensity—CIE 15:2004

The polyamide article color intensity “L” was measured by the standardized method CIE L*a*b* (standard CIE 15:2004 of the “Commission internationale de l'éclairage”). In this method, the polyamide article is assessed using a spectrophotometer or a colorimeter, and the L* a* and b* coordinates are obtained from the equipment. The luminosity coordinate “L” varies from 0 to 100, being 0 “black” and 100 “white”. The measurement uses the illuminant type D65, and 10° for the observation angle. The lower is this, parameter, the darker is the color.

1. Study of the Influence of the Dyeing Temperature and Cycle Time Comparative Examples 1 to 4—100% Polyamide 5.6 BR Synthesis or origin of the polyamide of the polyamide 5.6 BR

The polyamide 5.6 pellet is a commercially available polyamide from Cathay Biotech under the trademark Terryl®. It is a brilliant polyamide containing no titanium dioxide. The IVN (viscosity index) is from 138 to 142, and ATG (amine terminal groups) from 38 to 42, measured according to the methodology disclosed herein.

Synthesis of the Fiber and Article Based on the Polyamide 5.6 BR

A polyamide fiber was obtained during melt-spinning extrusion of the above polyamide 5.6 BR (Brilliant).

The multi-filament polyamide fiber obtained was further texturized into linear density of 2×80f68 dtex and knitted into fabric. The tenacity obtained was 30.0 cN/tex and elongation was 28.6%.The knitted fabric was dyed in exhausting equipment at:

Comparative Example 1—100° C.—60 minutes Comparative Example 2—70° C.—30 minutes Comparative Example 3—60° C.—30 minutes Comparative Example 4—50° C.—30 minutes

The quantity used was 3.5% wt of a black acid dye, and 1% wt of a leveling agent. The pH of the solution was adjusted to 3-4 with ammonium sulfate and acetic acid. The bath relation was 1:30, meaning 1 part of fabric per 30 parts of water.

Comparative Examples 5 to 8—100% Polyamide 6.6 BR Synthesis or Origin of the Polyamide 6.6 BR

The polyamide 6.6 pellet was produced at Rhodia Poliamida e Especialidades Ltda. It is a brilliant polyamide (no titanium dioxide) produced from the polymerization of a nylon salt containing mainly hexamethylenediamine and adipic acid. The IVN (viscosity index) is from 128 to 132, and ATG (amine terminal groups) from 40 to 45, measured according to the methodology disclosed herein.

Synthesis of the Fiber and Article Based on the Polyamide 6.6 BR

A polyamide fiber was obtained during melt-spinning extrusion of the above polyamide 6.6 BR (Brilliant).

The multi-filament polyamide fiber obtained was further texturized into linear density of 2×80f68 dtex and knitted into fabric. The tenacity obtained was 31.5 cN/tex and elongation was 28.8%.

The knitted fabric was dyed in exhausting equipment at:

Comparative Example 5—100° C.—60 minutes Comparative Example 6—70° C.—30 minutes Comparative Example 7—60° C.—30 minutes Comparative Example 8—50° C.—30 minutes

The quantity used was 3.5% wt of a black acid dye, and 1% wt of a leveling agent. The pH of the solution was adjusted to 3-4 with ammonium sulfate and acetic acid. The bath relation was 1:30, meaning 1 part of fabric per 30 parts of water.

Evaluation

Each of the comparative examples (1 to 8) is evaluated for washing fastness, alkaline and acid perspiration fastness, CIE Lab color intensity “L”, IVN (viscosity index) and ATG (terminal amino groups). The results are shown in the table 1 below.

TABLE 1 Dyeing Dyeing Acid* Alkaline* PA 5.6 PA 6.6 Time temperature Washing* sweat sweat IVN ATG BR BR [min] [C.] Color CIE “L” fastness fastness fastness 1 141 41 100% — 60 100 14.3 ± 0.2 4/5 4/5 4 2 141 41 100% — 30 70 14.2 ± 0.2 4/5 4 4 3 141 41 100% — 30 60 14.6 ± 0.2 4/5 4 3/4 4 141 41 100% — 30 50 15.1 ± 0.2 4/5 4 4 5 124 49 — 100% 60 100 14.9 ± 0.2 5 5 4/5 6 124 49 — 100% 30 70 15.2 ± 0.2 5 5 4/5 7 124 49 — 100% 30 60 18.4 ± 0.2 5 4/5 4/5 8 124 49 — 100% 30 50 30.0 ± 0.2 5 4/5 4/5 *Grade for color transference to the adjacent fabrics. The color change of the samples (not shown) was assessed as grade 5 (maximum) in all of the examples above.

Conclusion

From the comparative examples 1 to 4 (polyamide 5.6), the black color intensity starts to decay at temperature≤60° C., which means this is the minimum temperature of dying of dark colors, such as the black used for the experiments. Whereas for comparative examples 5 to 8 (polyamide 6.6), a sharp decrease of color intensity is already obtained at 70° C. It can be concluded that there is a 20° C. difference in dyeing behaviour between polyamide 5.6 and polyamide 6.6, when comparing example 4 and 6, where they achieved the same intensity (ex. 4=15.1 and ex. 6=15.2). Therefore, 60° C. is the optimum temperature of dyeing of polyamide 5.6 with dark shades.

Examples 1 to 8 above cannot be directly compared to the examples 9 to 12 below due to the difference in opacity. The full-dull polymer contains higher amount of titanium dioxide and therefore results in lighter shades than brilliant polymers, using the same amount of dye. Examples 1 to 8 are comparable within itself and are important for setting the optimum dyeing temperature and time for the invention. Whereas examples 9 to 12 are comparable within itself and show the advantages obtained by the present invention in terms of color uptake and fastness.

2. Tests with Reduced Dyeing Temperature and Cycle Time Examples of the Invention 10 and 11—Polyamide Blend

A polyamide fiber blend was obtained during melt-spinning extrusion. The first polyamide was the polyamide 6.6 FD (full-dull). This polyamide is prepared similarly to comparative examples 5 to 8 and it is full-dull (containing about 1.5% of Titanium dioxide). The second polyamide was the polyamide 5.6 (brilliant) as described above for comparative examples 1 to 4.

The second polyamide was continuously introduced during step al of the single-screw extruder as a polyamide pellet by means of a gravimetric feeding apparatus. In step a2, the polyamide blend was melted, homogenized and pressurized inside the screw extruder at a temperature of around 290° C. and at an extrusion pressure of around 50 bar. Then, according to step a3, the molten polyamide blend was spun into multi-filament yarn at a spinning pack pressure of around 200 bar and at a spinning pack flow rate of around 5 kg/h. At Step a4, the polyamide fiber blend was solidified and wound into bobins at 4200 m/min.

In example 10, the polyamide 5.6 was continuously added at step al as 5% weight of the total polyamide blend.

In example 11, the polyamide 5.6 was continuously added at step al as 10% weight of the total polyamide blend.

The multi-filament polyamide blends obtained were further texturized into linear density of 2×80f68 dtex and knitted into fabric. The knitted fabric was dyed in exhausting equipment at 60° C. temperature for 30 minutes. The quantity used was 3.5% wt of a black acid dye, and 1% wt of a leveling agent. The pH of the solution was adjusted to 3-4 with ammonium sulfate and acetic acid. The bath relation was 1:30, meaning 1 part of fabric per 30 parts of water.

Comparative Example 9—100% Polyamide 6.6 FD

A polyamide fiber was obtained during melt-spinning extrusion. The polyamide was the polyamide 6.6 FD (full-dull) as prepared/described above for examples 10 and 11.

The multi-filament polyamide fiber obtained was further texturized into linear density of 2×80f68 dtex and knitted into fabric. The knitted fabric was dyed in exhausting equipment at 60° C. temperature for 30 minutes. The quantity used was 3.5% wt of a black acid dye, and 1% wt of a leveling agent. The pH of the solution was adjusted to 3-4 with ammonium sulfate and acetic acid. The bath relation was 1:30, meaning 1 part of fabric per 30 parts of water.

Comparative Example 12—100% Polyamide 6 FD

The polyamide was the polyamide 6, FD (full-dull). This texturized polyamide yarn was obtained from the company Antex Ltda as a bobbin.

The multi-filament polyamide fiber was knitted into fabric. The knitted fabric was dyed in exhausting equipment at 60° C. temperature for 30 minutes. The quantity used was 3.5% wt of a black acid dye, and 1% wt of a leveling agent. The pH of the solution is adjusted to 3-4 with ammonium sulfate and acetic acid. The bath relation was 1:30, meaning 1 part of fabric per 30 parts of water.

In all of the examples above, a posterior fixation step was performed, using 3% wt of a fixation agent for 30 minutes at 80° C.

Evaluation:

Each of the examples (Examples 9 to 12) is evaluated for washing fastness, alkaline and acid perspiration fastness, CIE Lab color intensity “L”, IVN (viscosity index) and ATG (terminal amino groups). The results are shown in the table 2 below.

TABLE 2 Dyeing Dyeing Color Acid* Alkaline* PA 5.6 PA 6.6 PA 6 Time temp. CIE Washing* sweat sweat Tenacity Elongation IVN ATG BR FD FD [min] [C.] “L” ± 0.2 fastness fastness fastness (cN/dtex) (%) 9 130 43 — 100%  — 30 60 30.6 5 5 5 41.1 28.6 10 128 46  5% 95% — 30 60 24.6 5 5 5 39.8 25.6 11 129 46 10% 90% — 30 60 19.5 5 5 5 41.1 25.2 12 — — — 100% 30 60 24.7 — — — 38.0 28.4 *Grade for color transference to the adjacent fabrics. The color change of the samples (not shown) was assessed as grade 5 (maximum) in all of the examples above.

Conclusion:

In the case of the blend of the invention (ex. 10 and 11), the polyamide article was also effectively dyed at 60° C. for dark colors (ex. Black). According to the results, examples 10 and 11 achieved a more intense black color (L=24.6 and L=19.5 respectively) comparing to the control example 9 (L=30.6), by adding 5% and 10% of polyamide 5.6, respectively, during melt-spinning extrusion of polyamide 6.6, with half the time of a normal dyeing cycle, 30 minutes instead of 60 minutes.

This represents a considerable reduction in relation to a conventional boiling temperature, and proves that the same dyeing advantages shown by polyamide 5.6 can also be obtained with blends of polyamide 5.6 and polyamide 6.6.

In summary, low-temperature dyeing properties and shorter dyeing cycle are possible with polyamide 5.6 and polyamide 6.6 fiber blends. The resulting color fastness of polyamide blended articles (ex. 10 and 11) is also superior in relation to polyamide 5.6 articles alone (ex. 1 and 3). Furthermore, the dyeing property of the polyamide fiber blend is better than the conventional polyamide 6 (ex. 12). 

1. A polyamide fiber with enhanced dyeing properties, comprising a blend of at least: a first polyamide selected from the group consisting of polyamide 6, polyamide 6.6, polyamide 6.9, polyamide 6.12, polyamide 6.10, polyamide 11, polyamide 12, polyamide 10.10, polyamide 4.6, polyamide 4.10, polyamide 12.12, polyamide 10.12, and mixtures thereof, and a second polyamide selected from polyamides 5.X, wherein X is an integer from 4 to 16, and mixtures thereof.
 2. A polyamide fiber according to claim 1, wherein the first polyamide is selected from the group consisting of polyamide 6.6, polyamide 6, and mixtures thereof.
 3. A polyamide fiber according to claim 1, wherein the second polyamide is polyamide 5.6.
 4. A polyamide fiber according to claim 1, wherein the second polyamide is present in an amount of about 1.0% to 40.0% by weight of the total weight of the polyamide fiber.
 5. A method for obtaining making a polyamide fiber according to claim 1, comprising melt-spinning extrusion of a blend of at least the first and the second polyamide
 4. 6. A method according to claim 5, wherein the melt-spinning extrusion comprises the following steps: a1. feeding the first polyamide melt, pellet, or powder into the inlet of a screw extruder or grid spinning head, a2. melting, homogenizing, and pressurizing the polyamide, a3. spinning the molten polyamide into a fiber, and a4. cooling down and winding the fiber; wherein the second polyamide is continuously introduced during step al as a pellet or powder form.
 7. A method according to claim 5, wherein the melt-spinning extrusion comprises the following steps: a0. polymerizing diacid and diamine monomers or salts thereof to form a blend of at least the first and the second polyamides, a′1. feeding the blend of at least the first and the second polyamides as a melt, as pellets or as a powder into the inlet of a screw extruder or grid spinning head, a2. melting, homogenizing, and pressurizing the polyamide, a3. spinning the molten polyamide into a fiber, a4. cooling down and winding the fiber.
 8. A method according to claim 5, wherein the melt-spinning extrusion comprises the following steps: a1. feeding the first polyamide melt, pellet or powder into the inlet of a screw extruder or grid spinning head, a2. melting, homogenizing, and pressurizing the polyamide, a3. spinning the molten polyamide into a fiber, a4. cooling down the fiber and winding the fiber, wherein the second polyamide is continuously introduced during step a3 as a polyamide melt.
 9. A method according to claim 5, wherein the second polyamide is present in an amount of 1.0% to 40.0% 5.0 to 20.0% by weight of the total weight of the polyamide fiber.
 10. A method according to claim 5, wherein the resulting polyamide fiber is dyed.
 11. A method according to claim 10, wherein the polyamide fiber is dyed at a temperature from 40° C. to 80° C.
 12. A method according to claim 10, wherein the polyamide fiber is dyed with a dyeing cycle of from 20 to 40 minutes.
 13. A polyamide article comprising a polyamide fiber according to claim
 1. 14. A polyamide article according to claim 13, wherein the polyamide article is a fiber, a staple fiber, a flock, a woven, a knitted or non-woven fabric, or a textile article.
 15. A method according to claim 13, wherein the polyamide fiber is transformed by texturizing, drawing, warping, knitting, weaving, nonwoven processing, garment manufacturing or a combination thereof.
 16. A method to claim 13, wherein the polyamide article is dyed.
 17. A method according to claim 15, wherein the polyamide article is dyed at a temperature from 40° C. to 80° C.
 18. A method according to claim 16, wherein the polyamide article is dyed with a dyeing cycle of from 20 to 40 minutes.
 19. A method for enhancing the dyeing properties of a polyamide fiber, comprising blending a second polyamide selected from 5.X, wherein X is an integer of from 4 to 16, and mixtures thereof with at least a first polyamide selected from the group consisting of polyamide 6, polyamide 6.6, polyamide 6.9, polyamide 6.12, polyamide 6.10, polyamide 11, polyamide 12, polyamide 10.10, polyamide 4.6 polyamide 4.10, polyamide 12.12, polyamide 10.12, and mixtures thereof in order to enhance the dyeing properties of a polyamide fiber made therefrom.
 20. A polyamide fiber according to claim 4, wherein the second polyamide is present in an amount of about 5.0 to 20.0% by weight of the total weight of the polyamide fiber.
 21. A polyamide fiber according to claim 1, wherein the polyamide fiber has an overall dtex of about 40 to 300, and a dtex per filament of about 1 to
 5. 22. A method according to claim 10, wherein the resulting polyamide fiber is dyed with an acid dye.
 23. A method according to claim 16, wherein the polyamide article is dyed with an acid dye. 